Source: National Assembly For Wales / Cynulliad Cymru
Mr Andrews quit after being criticised for his defence of a school that faced closure under his own surplus places policy.
He had been pictured holding a banner in support of Pentre Primary School in Rhondda, where he is assembly member.
A decision on who will replaced Mr Andrews as education minister has yet to be made.
In his resignation letter, Mr Andrews told Carwyn Jones, the first minister, that he was a “passionate advocate of my Rhondda constituency”.
He added: “I regret that my commitment to my constituents may have led me to an apparent conflict which has led to difficulty to your government.”
In the letter, Mr Andrews also said he was “proud of the steps which we have taken which will strengthen the education system in Wales from schools through to higher education, including…the creation of a smaller number of stronger higher education institutions and our new HE policy”.
Mr Andrews had pushed through university mergers. Trinity University College and the University of Wales Lampeter merged in 2010 to create the University of Wales Trinity Saint David. Swansea Metropolitan University is now also merging with the institution.
Meanwhile, the University of Glamorgan and the University of Wales, Newport have also merged, although the Welsh government backed off from forcing Cardiff Metropolitan University to merge with them after objections from the institution.
In December 2011, Mr Andrews said the latter merger would create “an institution with real critical mass, a strong overseas recruitment driver and with a deeper and stronger research base”.
He said Wales had to choose between a “market route” taken by England or a “smaller number of stronger universities” that could be brought about through mergers.