Here's another expression which is beyond my understanding in this context.
海外で暮らす日本人のお母さん方のいちばんの不安は、子供の日本語学習が遅れることです。
しかし、ここで国語のドリルなどをやっても力はつきません。
解く勉強や書く勉強は、形が残るので勉強をしている気になりますが、その分絶対量が不足するのです。
What I think the text is saying is that by just doing standard exercises with paper and pencil (writing and solving various problems etc), the total amount of exposure to the native language will be insufficient (for proper development) for a child living abroad. I still don't understand what a method of studying where "形が残る" actually is though. Only thing I can think of is that writing and answering things on a test paper produces something "visible and structured" and therefore leads to a greater inclination towards studying, but this is one of many instances where japanese is stretching my logical capacity.