The Welsh government has been forced to delay its controversial banding system for primary schools by more than two years after opposition from teachers.

The scheme, which groups schools into five bands based on performance and attendance data, was due to be launched at Easter. But earlier this week, education minister Leighton Andrews said there were not enough “robust data” to properly calculate the bands and announced that the launch would be delayed until September 2014.

Teaching unions praised the minister for listening to teachers’ concerns and for making a “brave and wise” decision, but opposition parties called it an “embarrassing U-turn”.

Teachers and local authority officials had expressed concern about the primary banding system because schools were to be banded based on their end of key stage 2 assessment results.

Estyn, the Welsh inspectorate, called into question the reliability of the tests two years ago, and in chief inspector Ann Keane’s annual report last month it said almost half of the 238 primary schools inspected since September 2010 had aspects of assessment that were weak.

Mr Andrews said the scheme would be delayed until national reading and numeracy tests - currently being developed - were introduced.

Teaching unions welcomed the news. ATL Cymru said it was a “wise and brave” decision by the minister and NUT Cymru said he should be “applauded”. Heads’ union NAHT Cymru congratulated the minister on his willingness to listen.

But Plaid Cymru education spokesman Simon Thomas called it an “embarrassing climb-down” and urged the minister to abandon the idea completely.

The Welsh government has faced opposition to its banding plans from the beginning. Critics have denounced them as being league tables in disguise.