It isn't just appropriate level, it is appropriate method and rate of instruction, too.

I wish the word pedagogical term acceleration actually meant acceleration. If a car is travelling a constant 100mph to a destination city 1200mph away and teleports instantaneously 200 miles towards the destination. Even though it's average rate of travel has increased, it has never accelerated. Even compacting misses the point. Though it seems like grade skipping and compacting can help.