Every May, all schools in Wales are required to undertake the National Tests as set out by the Welsh Government. The tests apply to pupils who are in Years 2 - 9 during the test window, which is the end of April / beginning of May. There are 3 tests: Reading, Mathematical Procedural and Mathematical Reasoning. Each year the Welsh Government produce a guidance booklet for parents which gives you everything you need to know about the tests. You can download this years below:
The results of the National Tests are usually available towards the end of the summer term, parents will get a double-sided A4 report with the results to all the tests. There is a short video which you can watch below, this will help you to understand how to interpret the results.