Minecraft Education Worlds cannot be imported into Minecraft Bedrock without changing the NBT tag, eduOffer, to 0. If you open a Minecraft Education world in an NBT Editor and scroll to eduOffer, it will be 1, while for Minecraft Bedrock worlds, the eduOffer NBT tag would be 0. It is a very frustrating bug, and I hope it gets fixed. This is a very big issue for Minecraft Education Edition users (which are basically students, educators and teachers like me) since when they leave the school or graduate from that school, their school accounts would be deleted, and if their school accounts are deleted, your Minecraft Education worlds are deleted since you no longer have access to Minecraft Education Edition.

Especially when it is 'education edition', students take time to create big builds as their assignment (or for fun) and it is unfortunate to loosed days, weeks, months, and even years of progress when the students leave or graduate from the school. 

Since Minecraft Education Edition doesn't mention and talk about world editors and NBT editors that much, Minecraft beginners(students) might not know what NBT editors are.

How to reproduce this bug:

1: Make a Minecraft Education world.

2: Export the Minecraft Education world to Minecraft Bedrock.

3: If you import Minecraft Education Worlds into Minecraft Bedrock, it will fail no matter what without NBT editing.

How to import a Minecraft Education world to Minecraft Bedrock with an NBT editor:

1: Open your Minecraft Education world in an NBT Editor

2: Change the NBT tag eduOffer from 1 to 0, since 1 would represent a Minecraft Education world, and save the changes.

3: Import the modified Minecraft Education World to Minecraft Bedrock.

4: Yay, you have done it. Now the Minecraft Education world should import into Minecraft Bedrock.

I personally tried this by myself, and it worked.