Research by the Early Intervention Foundation (EIF) and the Education Policy Institute (EPI) has found major gaps in evidence to underpin early years policies, despite £6bn worth of government investment by 2019/20 on initiatives such as 30 hours of funded childcare for three- and four-year-olds in working households.
Their concerns are outlined in two reports, with the EPI looking at issues such as the qualifications of early year staff and child-to-teacher ratios, while the EIF focuses on the day-to-day activities children take part in.
The EPI report found that there is a particular need for more robust evidence on the value offered by early years staff with a degree.
It also found there is "very little rigorous research" on the impact that small child-to-teacher ratios and class sizes have. This is particularly the case in reception year classes where more knowledge is needed about whether large classes divided into small groups can improve learning.
"The existing evidence on what is meant by high quality is dense, poorly understood, and inaccessible to practitioners, commissioners and policy-makers," states the EPI report.
It adds: "Overall, a lack of strong evidence about what works best, and failure to embed this knowledge in the early years system, leads to a lack of coherent structure to problem solving and a sub-optimal use of resources."
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The EIF report looks at the impact of 83 different teaching programmes and practices in early years settings. It found that the majority of evidence came from the US not the UK and also lacks detail about specific issues such as different teaching materials used.
The long-term benefits for children of particular teaching practices as well as their impact on different groups of children, including those from disadvantaged backgrounds, is also lacking.
"Although many programmes were targeted at disadvantaged children, few studies tested variation in the impacts for different groups of children," states the EIF report.
"Therefore, it is not possible to conclude whether particular programmes or interventions might be more effective for certain groups."
Pre-school Learning Alliance chief executive Neil Leitch said that the reports "raise important concerns and the serious gaps in the evidence being used to underpin the development of early years policy".
He added: "If the government is truly is committed to supporting young children's learning, and particular those from more disadvantaged backgrounds, it must ensure that these evidence gaps are filled.
"Our youngest children deserve an early education built on what has been proven to work, not one hampered by government schemes and initiatives launched primarily to secure votes and positive headlines - something that we seem to be seeing more and more often in recent years."
Children and Families Minister Nadhim Zahawi said: "We want every child to have the best start in life which is why we are spending more than any other government on supporting early years education and childcare - around £6 billion a year by 2020. And we're seeing improving outcomes in the early years - the proportion of children achieving a good level of development by the end of reception increased from 60 per cent in 2014 to 70 per cent last year.
"There are no great early years settings without great professionals working in them, which is why we want to continue to attract the brightest and the best. This ambition is backed by £20 million to provide training and professional development for early years staff in disadvantaged areas to increase their ability to support children's early speech and language development. "