Taking this idea seriously for a minute, and only for the UK, a number of possibilities suggest themselves, and I am ignoring all pre-1960 initiatives that many, including Keith Wheeler in 1975 in Insights into Environmental Education, wrote about ...
– the 1960s which saw Silent Spring and the advent (in 1968) of the Council for Environmental Education [CEE] and the Society for Environmental Education [SEE] (in 1969). Neither survives.
– the early 1970s which saw the IUCN conference in Nevada, and when BEE was first published, the Schools Council set up Project Environment, and the National Rural Studies Association was formed (later to become NAEE in 1972). The last does survive.
– the mid 1970s when, following the publication of the Club of Rome (in 1972) report (Limits to Growth), university degrees in environmental subjects were launched along with GCE O and A level examination courses in environmental science and environmental studies. The former persist but the latter are long gone which is a pity as some were commendably in-depth explorations of issues which are as pertinent today as then. They were killed by the desire for uniformity in the national curriculum and by the shift to GCSE.
– the late 1970s which saw DfE interest and serious engagement from HMI which produced its own environmental education curriculum reports which are useful documents today. This was the time of the Tbilisi Declaration and great international interest in environmental education. Although the DES published Environmental Education in the UK as its contribution to Tbilisi, mainstream schooling remained largely unaffected.
– the late 1980s and the first Great Debate about the curriculum. Sadly, environmental issues were far from the minds of those leading the debate which was mostly about (raising) standards, presaging the interests of today; indeed, it began a period which we are still living through.
– 1990 when the National Curriculum Council published Curriculum Guidance 7 which set out the aims of environmental education along with case studies and classroom activities. This was welcomed as a lifeline by teachers desperate to escape the conformity of the national curriculum as it provided some renewed legitimacy for environmental education – but only as a cross-curriculum theme. Those who knew what had been lost were not fooled.
– 1995 and the launch of Environmental Education Research. This is a great success, but was a Faustian bargain as it has been instrumental in ensuring that EE research rarely reaches mainstream education research audiences.
– 1996 when both the Secretary of State at the Department of the Environment and the Secretary of State at the Department of Education both appeared on a platform promoting environmental education. Happy daze, but the warm glow quickly faded.
– the early 2000s which saw the sustainable schools initiative and all those doorways (colourful cartoons and rainbows). This was remarkable because it came from the DfE (or whatever it was called then). People who might know better remember all this fondly, but we need to recall that there was no space in all this for biodiversity; not did it influence the DfE's mainstream educational policies. Those windows were all slammed shut by the advent of the Coalition government in 2010 when the standards agenda resurfaced.
– etc, etc ...
Of course, there was no golden age after which everything was somehow lost, and there's no sign of one emerging anytime soon. Although if you re-examine the early projects that are mentioned here (and there were many more), it's easy to see the momentum that has been dissipated, but what it does provide is a background against which our current predicament can be viewed, and, for example, the recommendations of the recent King's report.