In 1973, she took her first teaching post, at Holland Park School, a comprehensive in Kensington and Chelsea which was then part of the Inner London Education Authority, where she taught French.

With the threatened break up of the ILEA, Blower moved back to Hammersmith and Fulham in 1990 and concentrated on working with young teenagers at risk of care or custody at Farm Lane Adolescent Resource Centre.

Blower used this platform to argue for a greater role for teachers in the running of Pupil Referral Units and for "properly resourced nursery provision".

[5] After the sudden death of Sinnott while in post,[6] she became acting general secretary on 5 April 2008,[7] and led the union's first national strike in two decades – over teachers' pay – a fortnight later.

Blower has aligned herself to long-standing NUT criticisms of the standard assessment tests (or SATs) in schools, including the national boycotts led by the union in 1993[11] and 2010.

Blower has referred to the tests as "high stakes", with teachers under pressure to narrow the curriculum, "skewing everything to enable their pupils to jump through a series of unnecessary hoops".

[14] Under Blower's leadership, the NUT has published its proposals for alternative approaches to assessment, most recently in conjunction with the NAHT in 2009[15] and with ATL in 2010.

[17] In her presidential address to NUT Conference on 29 March 1997, Blower reported that in the previous year her daughter Sophie had been withdrawn from the Key Stage 2 tests.

The NUT opposes Free Schools[22] and Blower has voiced concerns that they are able to employ teaching staff without Qualified Teacher Status.

Blower has disputed the success of the Swedish system as well as American charter schools,[24] both regularly cited by Michael Gove as exemplars of narrowing the social divide.

[25][26] In a cover story for The Spectator magazine in August 2010, it was claimed that NUT activists were "bullying" head teachers known to be considering academy conversion and, with it, a break from local authority control.

In March 2016, ahead of her departure as general secretary of the NUT, Blower announced that she would be joining the Labour Party "led by Jeremy Corbyn, to fight for the better world we know is possible".