## 3 Results
### Evidence of Efficacy  
The results are reported in detail in Table 2; Table 5 reports the main findings of the studies examining the efficacy of the SG training. The results show that in all the studies, a significantly higher improvement in reading skills was observed in the group treated with SG compared with the control group, with only a few exceptions. The first was [36], in which the advantage of the group treated with SG with respect to the control group was evident only in the children with high self-efficacy that used reading SG. The second was [34], which found a greater reading gain in the group trained with SG than in the control group only in the reading of long and complex words, and not in the reading of simple and short words and pseudowords, as well as in phoneme-grapheme mapping. However, it should be noted that this study [34] was conducted on German children, who learn a highly consistent orthography, in which sublexical difficulties in reading relatively easy and short stimuli are generally less marked. This may have contributed to making the improvements less noticeable under the simpler conditions, compared with more difficult conditions, such as the reading of long and complex words.  
Improvements in reading comprehension were investigated in only four studies, of which three [34; 35; 38] found no major improvement following training with SG, while one [37] found a significant effect on text comprehension. However, it is important to specify that none of the studies apply SGs as training for reading comprehension of meaningful sentences or texts.  
Spelling improvement was investigated in only three studies [34; 35; 38], showing that the SG training did not produce greater improvements in writing than those found in the  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**ID** & **Authors** & **Spelling** & **Reading** & **Reading** & **Language** & **Metaphonological** & **Engagement** \\ \hline
1 & [PERSON] et al. (2016) [32] & N/A & + & N/A & N/A & N/A & + \\ \hline
2 & [PERSON] et al. (2020) [34] & – & +/– & – & N/A & +/– & + \\ \hline
3 & [PERSON] et al. (2019) [35] & – & + & – & N/A & N/A & + \\ \hline
4 & [PERSON] et al. (2020) [36] & N/A & +/– & N/A & N/A & N/A & N/A \\ \hline
5 & [PERSON] et al. (2019) [37] & N/A & + & + & + & N/A \\ \hline
6 & [PERSON] et al. (2021) [38] & – & + & – & N/A & N/A & N/A \\ \hline \hline \end{tabular}
\end{table}
Table 5: Efficacy of SG training. Plus (+) indicates a statistically significantly larger improvement in the group trained with the SG compared with the control group; Minus (–) indicates similar gains in experimental and control groups; Plus/Minus (+/ –) indicates a larger gain improvement after SG training but limited only to specific circumstances.  
control group. In any case, including the improvement of spelling, it is important to note that none of the studies trained spelling skills with SGs, except for [32], which trained children to colour a letter shape on a screen by filling the gap with their fingers.  
Improvements in phonological awareness were investigated in [34; 37], showing a greater benefit of SG training, but only for more sensible measures and not for tasks that are usually easy in consistent orthographies, such as syllable counting and vowel length. Language was investigated only in [37], through the task of naming and word comprehension, showing greater gains in the experimental group.  
It should be noted that only one study reported follow-up data [35], but only for the experimental group and these data covered three months. The children were nevertheless able to maintain their achieved level in reading and spelling over the three months after the intervention. However, the lack of a follow-up for the control group prevented us from drawing a conclusion as to the long-term effects of SG interventions.