It is a big discussion in the Montessori community. Some montessorian love my apps, some wants kids to play only with wood objects... Nobody knows what would think Maria Montessori but since she was an innovator, I think she would be open-minded and uses all the tools that can help kids to learn. If you check my last app about tracing letters, the sense of touch coming from the sand paper has been replaced with sound (another sense). Anyway, I say it again: the iPad is just another tool, it does not replace all the existing materials.