Uteach teachers work through the agency for the first 1 or 2 terms to give both the teacher and the school time to assess each other and make sure it is the right teacher in the right job before any long term or permanent decisions are made. Both sides have a flexible contract during this period, although more often than not the temporary contracts become permanent.
As school budgets are constantly going through changes, a flexible work force makes it easier for schools to plan. Over the year, there is very little difference in cost to the school between taking the teacher directly or taking the teacher through a contract with Uteach. This is why so many schools take up the contract option.