The Association of Teachers and Lecturers (ATL) is calling on the government to reverse moves to "overly formalise" children's first few years of school and instead encourage the use of play-based learning techniques.
In a written submission to the education select committee, ATL said that schooling for children up to the age of seven "should be based on good early years principles, aims and practices that are developed by professionals and given cross-party support in government".
The submission to the committee's scrutiny of the government's response to its inquiry into the school starting age also called for more flexibility to be built into the education system so that it focuses on giving young children the best start in life.
The submission added: "School-based early years provision is becoming increasingly formal because of changes to the foundation stage curriculum, downward pressure from the new national curriculum and from the focus on phonics, and because changes to assessment within and beyond the foundation stage.
"This leads to the problem that school starting age becomes a cliff edge rather than offering the flexibility that some children and families need."
Currently, children start school at the beginning of the academic year after their fourth birthday, but some education experts believe this disadvantages very young children.
Last month, the shadow education secretary, Tristram Hunt called the Green Party a “flashback to the 70s” after criticising their manifesto, which contained a policy planning to delay school starting age to the age of six.
But Mary Bousted, ATL general secretary, added: “By introducing a baseline assessment and continuing with the phonics test, government continues to narrow and overly formalise the foundation stage curriculum and heap unnecessary pressure on four- and five-year-olds.”
The ATL also wants to see play-based learning and specialist early education knowledge incorporated into teacher training.
Bousted added: “School leaders should have a strong understanding of how the youngest children learn and develop. Initial teacher training should offer routes to qualified early years teacher status that include strong subject and pedagogical knowledge.
“All those who are training to teach or to lead should learn about child development, play-based learning and assessment through observation.”
The education select committee is now evaluating evidence received by the DfE with help from comments submitted to an evidence check forum, which closed yesterday.
The Department for Education has been contacted for comment.