I'm wary of any educational information coming out of the USSR. Good to know, though. It makes sense that trying to force development where the child isn't ready for it will cause them to struggle.
If it makes any difference, the information I got was from ex-USSR citizens who went through the process as kids and then raised their kids in the US system. It's been corroborated by both Russian professors (of the Russian language) and engineers in the aerospace industry.