The students will change the password and add new apps and play games they shouldn't be playing. I don't like them be because they will change the tab so they can play games and the teacher will not be able to see what is happening. With computers, the teachers can see what the students are doing.
Tablets are great. They are great for quick research, portability, etc. However, they aren't very efficient when it comes to word processing. There are some word apps, and some keyboards built for tablets. However, the programs aren't the greatest. Students need to learn how to get word processing done quickly and efficiently, and right now, computers provide the best option.
I do not believe that tablets can replace computers in schools. If they were to replace computers, then you would lose the ability to have a keyboard and to print from your device in some cases. The hardware inside of a tablet is also not nearly as robust as a dedicated computer. For now, we should stick to computers inside of schools.