2.1. Scaffolding in Education: Theory and Applications in Online Learning
The term “scaffolding” originated in the construction field, referring to temporary structures that support buildings [
9]. In education, scaffolding is primarily defined as providing appropriate assistance to learners, enabling them to solve challenging problems that they cannot tackle on their own [
10,
11]. Researchers attribute scaffolding to Vygotsky’s Theory of Social Constructivism and the concept of the “Zone of Proximal Development” (ZPD) [
12]. According to Vygotsky’s Social Constructivism, interaction with teachers or peers can help learners reduce cognitive loads and facilitate cognitive processing [
11]. This interaction is particularly beneficial for students to grasp new concepts within their Zone of Proximal Development. In the context of online learning, providing scaffolding support for learners, such as providing learning guidance, feedback, and assisting learners in communication and cooperation, etc., is useful for students to learn knowledge, and their learning satisfaction will be improved [
13,
14,
15].
2.2. Meta-Analyses Related to Scaffolding in Online Learning
It is a widely held view that scaffolding contributes to learners’ cognitive and non-cognitive development. For instance, scaffolding gives an impetus to students’ cognitive development [
5,
16], affective development [
17,
18], and facilitates the development of metacognitive awareness [
19,
20]. What is more, with learning support, students can become more autonomous. Despite theoretical support, the research results on the impact of scaffolding on students’ online learning performance are mixed. Therefore, some researchers try using a meta-analysis to integrate the findings of multiple studies to explore the impact of scaffolding on students’ online learning performance [
21,
22].
An early review of scaffolding in online learning was conducted by Jumaat and Tasir [
22]. They emphasized the positive significance of online scaffolding on learning reflection, active learning, and group cooperative learning, suggesting that scaffolding can help improve students’ learning performance. They identified four main types of scaffolding in the online learning environment: procedural scaffolding (guide learners in using learning resources or providing guidance on tool usage), conceptual scaffolding (assisting learners in identifying what to learn, such as providing a knowledge outline that presents information and logical relationships between concepts), strategic scaffolding (providing alternative ways to complete tasks, and a well known example is creating forums to help learners to communicate and address issues), and metacognitive scaffolding (supporting learners in assessing their current learning level, for example, using quizzes to check the level of learners’ knowledge).
A second meta-analysis was conducted by Doo et al., which compared online learning performance between scaffolding and non-scaffolding approaches, and it examined the impact of scaffolding design on students’ online learning performance [
21]. They found that scaffolding significantly improved online learners’ learning performance (effect sizes ranged from 0.660 and 1.072). In addition, it was found that the type of scaffolding, source of scaffolding, learning outcomes, and disciplines context had a significant mediating effect on learning outcomes. These findings show that: (a) scaffolding can be a powerful medium to promote learners’ online learning effect; and (b) scaffolding design plays a crucial role.
However, the above-mentioned meta-analyses were limited in some ways. Firstly, the review conducted by Jumaat and Tasir is a narrative review, which may be subjective to some extent, as it is written based on the author’s viewpoints, knowledge, and experience, making it susceptible to author preference [
22]. In addition, when the number of studies grows dramatically, to accurately synthesize the existing research results in narrative review is impossible. Secondly, existing research does not focus on the effect of scaffolding on online learning in primary and secondary schools [
21,
22]. Thirdly, the existing research conclusions may be subject to debate due to the great progress in technology in recent years, which may influence the effectiveness of scaffolding for online learning [
21,
22].
2.3. Moderating Factors Influencing the Effect of Scaffolding in Online Learning
At present, there is no conclusion about whether scaffolding can improve students’ online learning performance. One possible reason is that scaffolding may play different roles in different online learning situations. It is necessary to investigate the variables that may moderate the effect of scaffolding in online learning.
Scaffolding may have different impacts on different disciplines. Lin et al. designed an adaptive guidance (meta-cognitive scaffolding) to help students learning computer knowledge and found that the scaffolding significantly improved students’ learning effect [
23]. Bannert and Mengelkamp used meta-cognitive scaffolding to assist students in learning psychological knowledge, but they found that scaffolding does not have a positive effect on knowledge learning [
24]. Therefore, we can hypothesize that some disciplines may be more connected with scaffolding than other disciplines.
Another personal characteristic that can be used as the moderator of scaffolding effect in online learning is grade level. For example, to promote reading comprehension performance of primary school students, Chen developed an online collaborative reading annotation system to assist students in online reading, and the result shows that the effect of scaffolding on students’ performance is 1.04 [
25]. Abdelaziz and Zehmi designed a cognitive scaffolding to provide students with audiovisuals and picture materials, help students interact and provide timely feedback, etc., so as to help underachieving learners in middle schools to solve problems in English grammar learning. They found that the effect size of scaffolding on learners was 0.53 [
26]. There is a large difference in effect size between the two studies. Therefore, we hypothesize that scaffolding in online learning might have different results for different grade levels.
The effectiveness of scaffoldings on different online learning outcome types is unclear. Scholars have reported the effects of scaffolding on knowledge learning in the cognitive domain, the affective domain, and the metacognitive domain. Yu and Pan explored the effects of problem generation scaffolding on students’ academic achievement (cognitive domain), problem generation performance (cognitive domain), learning satisfaction (affective domain), and learning anxiety (affective domain) in online learning. They found that scaffolding is useful for learning knowledge in the cognitive domain, but it was ineffective in learning knowledge in the affective domain [
8]. Avcı revealed that scaffolding is beneficial to developing students’ meta-cognitive skills [
27], while Bannert and Mengelkamp drew the opposite conclusion [
24]. Does scaffolding have different effects on knowledge learning in the three domains? If so, we can take the learning outcome types as a moderator variable to understand how scaffolding affects different learning outcome types.
Learning modes (individual online learning vs. collaborative online learning) may be important factors affecting the effect of scaffolding in the online learning environment. For example, Tegos and Demetriadis provided a conversational agent to assist students’ online collaborative learning, and results show that it can significantly improve students’ online learning performance [
28]. Some studies reached a similar conclusion [
18,
29]. Casselman, Eichler, and Atit provided scaffolding for personal study and found that scaffolding had little effect on improving students’ learning performance [
30]. Yu and Pan also reported similar conclusions [
8], but other researchers have come to the opposite conclusion [
17,
26]. Therefore, it is necessary to explore whether scaffolding plays the same role in different online learning modes.
The effect of different scaffolding types in online learning is unclear. Kao, Chiang, and Sun customized a digital game and designed demonstration scaffolding (strategic scaffolding), and they marked critical feature scaffolding (conceptual scaffolding) to evaluate its effects on learning [
31]. They found that conceptual scaffolding is better than strategic scaffolding in improving students’ conceptual knowledge learning. A message tag (procedural scaffolding) and sentence opener (meta-cognitive scaffolding) were designed by AK to assist students in sending messages in online collaborative learning, and the influence of these two scaffoldings on students’ learning results was explored. It was found that both scaffoldings had no influence on students’ learning results [
32]. These findings indicate controversies regarding the effect of different scaffolding types on learning outcomes. Therefore, it is necessary for us to explore whether scaffolding types will affect the results of online learning.
In this meta-analysis, we discussed whether learning disciplines, educational levels, outcome types, learning modes, and scaffolding types will influence the effect of scaffolding on students’ online performance. The results can assist in finding the factors that affect the effect of online scaffolding.