Head teachers should not be treated like football managers and face the sack if they have a bad year, union leader Mike Welsh has warned.
The National Association of Head Teachers president criticised what he called education's "quick fix" and blame culture.
He told NAHT's conference that creating a good school took time.
The union is also unhappy with national schools tests in England and is boycotting this year's ones.
These exams, known as Sats, are due to take place in just over a week.
Results from the national tests - in English and maths - are used to make up the primary school league tables and underpin reports by Ofsted inspectors.
Mr Welsh told delegates at the conference in Liverpool: "Seeing a quick data fix by pushing children through hoops does not embed learning.
"We must move away from the football metaphor of saying that unless the manager achieves promotion this season then they should face the sack."
Instead, the government should trust schools and head teachers to raise standards, he said, and offer support rather than sanctions if they struggled.
"Schools are organic, as with all organisations. Over a few years we can be on top form some of the time and pretty good most of the time and occasionally have a hiccup.
"Just at the time the school might want some support… along comes Ofsted and instead we get a punitive, clunking fist which demoralises rather than enthuses.
"It talks of raising expectations and then only uses the big stick to do this."
Mr Welsh told the conference Sats humiliated school leaders through the league tables and that some head teachers had lost their jobs "directly due to the use of Sats data as the basis for inspection".
"Assessment has to be proportionate, fair and supportive," he said. "Accountability should not be destructive by being permeated by a lack of trust."
He also said that the standard of people entering the profession had to be upheld as more people turned to teaching during the recession.
"With the economic downturn some are looking for shelter until the storm abates. We must remain a vocational profession with the highest calling," he told delegates.
Speaking beforehand, Mr Welsh said: "We have got to say that coming into teaching is more than just a short-term job."