The skills needed to teach primary children should not be underestimated, MPs heard.
Some teachers are beginning their careers in primary schools with as little as a few hours training in some subject areas, MPs have heard.
The Education Select Committee heard how the brevity of initial teacher training in England meant continuous professional development was vital.
But much of it focused on new regulatory requirements and curriculum shifts, rather than subject areas.
Ministers are changing teacher training to have more based in schools.
Professor Jane Courtney of the Deans of Education Network at the higher education think tank, Million+, said the biggest problem was in primary schools.
Whereas at secondary level, teachers were trained in one or two subject specific areas, at primary they were trained to cover 16 to 17 curriculum areas, she said.
"If we look at some of these areas we could be sending people out with as little as three hours taught input in a subject like PE.
"What primary schools have to do - they know their staff are undertrained - is provide CPD (continuous professional developments) for PE or provide coaches.
"Children are getting fragmented education with a little bit of coaching from this person and a little bit from someone else."
This led to a lack of progression and a lack of consistency, she said.
Andy Mitchell, Design and Technology Association assistant chief executive, said four hours' worth of training for design and technology for primary school teachers was not unusual, and said schools were not keeping up with recent developments in the subjects required by the new national curriculum.
"Stuff in the new GCSEs - the vast majority of design and technology teachers know nothing about," he said.
"The reason why it is worse now and it was never quite like that before is because we will not be able to rely on large centres of research and development - Keele, Loughborough, Nottingham-Trent, Exeter - all of these have withdrawn from initial teacher training education [for design and technology]."
Rewire a plug
This meant that staff who used to "rub shoulders" with academics at the forefront of research were no longer involved in teacher training, he said.
Robin Bevan, head teacher of Southend Boys School, said nearly all CPD currently being provided was based on keeping staff up to date with regulatory changes, statutory frameworks, curriculum changes or Ofsted requirements.
Very little focused on professional expertise or subject knowledge, which was what was needed, he said.
Prof Courtney said the need for highly trained primary school teachers should not be underestimated.
She said: "You can train somebody to rewire a plug.
"It's not quite so easy to train someone how to teach the concept of probability and what that looks like at age five to 18, and unpack it all.
"There's an assumption that because we are teaching children age five or six, that you don't need that much knowledge and of course you do to be able to tackle misconception upon misconception."
The Department for Education said in a statement: "Primary teachers have always taught a range of subjects and are not expected to be subject specialists.
"Providing the best possible training is at the heart of the government's drive to improve teaching standards, ensuring that all children, regardless of background, have the opportunity to fulfill their potential.
"Our review of initial teacher training (ITT) will ensure that trainee teachers can demonstrate good subject and curriculum knowledge across different subjects, and we have committed to go further by replacing qualified teacher status (QTS) with a new, stronger accreditation system to raise the bar for new teachers."