David Evans, Secretary of the National Union of Teachers (NUT) Cymru, said they back the comprehensive schools system fully.
He said "it suits us - its suits the people of Wales - it suits the children of Wales."
The last grammar school in Wales closed in 1988, but the Welsh Conservatives are calling for a return to the grammar system.
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Williams has had scans after he suffered a shoulder injury against Northern Ireland.
Chris Bryant was speaking on ITV's Good Morning Britain following his resignation as Shadow Leader of the House of Commons.