Unable to join others' worlds - Using Android tablet

My son is using Minecraft Education for school. His friends all have Apple IPADS and he has a Samsung tablet. He cannot join their worlds and I am wondering why it's so difficult for an android user to join worlds/ even download the app compared to apple users? Any help you can provide would be great as he is worried he's going to fail in their task as he can't play with the other kids in his class.