Most adults need a break after about 20 minutes of concentration. Try to interest your child in what she is doing If your child is interested, she will concentrate better. Children do develop natural interests in some things, but most of the time they learn to be interested by sharing the enthusiasm of others around them. Your own interest in what your child is doing helps develop her interest. Interest becomes motivation.
Motivation helps concentration.
If you want your child to concentrate better on those tasks she is not naturally interested in, your interest will help. Praise more than criticise Your interest on its own doesn't guarantee the interest of your child. Your interest could be so great that you become frustrated with your child and start to criticise her. Interest plus praise is very powerful, though. As adults, many of us don't like bosses who are 'always finding fault'.