"Preposterous" target setting and a formal academic curriculum are damaging children, says Wendy Scott, chief executive of the British Association for Early Education.
Addressing a Liberal Democrat special conference on education this week, she said that the current formal emphasis should be replaced by a new "foundation" key stage of play learning.
The Lib-Dems are committed to ending formal learning for under-fives. Education spokesman Don Foster said: "Whilst beginning to accept the importance of early education, the Government hasn't addressed the issue of quality. Because cramming yet more small children into overcrowded reception classes is not about quality."
Last week, Professor Kathy Sylva, a key government early-years adviser, called for a new "social curriculum" for under-fives, combining literacy, numeracy and science with personal and social education.