The purpose of the present study is to examine the effects of an intervention in which mathematics e-book (EB) activities were supported by metacognitive scaffolding on kindergarten children's mathematics knowledge and mathematics reasoning. Participants were 60 Israeli children who studied in three intact kindergarten classrooms in the Arab sector (age 5-6 years old). The kindergarten students were randomly assigned to three research groups, 20 children in each group, as follows: (a) using a mathematics EB; (b) using the same EB supported with metacognitive scaffolding (EBM); and (c) a control group who studied with no EB and no metacognitive scaffolding. Results indicated that the EBM group significantly outperformed the EB and control group on both mathematics reasoning and mathematics knowledge; the EB group significantly outperformed the control group on mathematics reasoning, but the differences between the EB and control groups on mathematics knowledge were not significant. Educational implications of the study are discussed.