他很高。 He is very tall.(An objective statement.) 他高高的。 He is tall.(It's often used in another person's memory,so it's subjective which means it's not so accurate and up to date.) 在我记忆中他是个高高的男生。In my memory,he was a tall boy.
I think you could show your teacher about my reply.Actutally,most of the time,even“很”doesn't really means "very".For example,we will never say 他高，the 很here is more likely to make short sentences sound not so weird.