When children work quickly the teacher gets her to help the other children. One of the children that dd has been helping had a statement for a full time one to one. There are two TAs in the classroom so there should be enough adults to help the class. Even a very able five year old has insufficient numeracy and literacy skills to make an effective TA. They might teach the concept incorrectly. Dd's spelling is still very phonics based.
I feel the teacher should have extention work for children who finish early. Children who need additional help should have the right to help from someone who has completed their education and is over 18!