There are certain recognisable phrases that can easily date a teacher - and strike chords of recognition, or produce faces of puzzlement. 

With everything from the integrated day to the miptor having special significance for a small section of the teaching community, there are plenty of trends that have come and gone and still bring back memories - good or bad - for some. 

This year marks the 25th anniversary of the start of one of those notable phases. For teachers of a certain age, the mnemonic of “15-15-20-10” has a special significance that they won’t quickly forget. For some, it sends a shiver down the spine.

For those not so familiar with the phrase, it referred to the time allocations in the nationally stipulated literacy hour, which arose from the 1996 National Literacy Project. 

Literacy hour: the impact it’s had on schools

In virtually every class in the land, teachers planned their lessons around the same structure: 15 minutes of whole-class text work, 15 minutes of word or sentence work, 20 minutes of independent tasks (with one group lucky enough to work with the teacher) followed by a 10-minute plenary. And woe betide you if you didn’t wrap things up 10 minutes before breaktime for this hallowed time.

From a comfortable distance, it’s both fascinating and chilling to consider the tight structure of the literacy strategy, and the impact it’s had on schools. 

For a start, it seems remarkable to consider now that there was ever a time when primary schools didn’t have a daily English lesson of at least an hour. Indeed, it’s not unusual to find 90 minutes or more dedicated to English in the daily timetable.

Yet in 1998, when the strategy was rolled out nationally, this was part of the reason for the disapplication of the national curriculum in other subjects. And there’s no denying that there was a significant increase in curriculum specification, from a few pages of the national curriculum to more than 50, setting out the termly objectives for the literacy hour.

The idea that there would be a centrally determined structure for lessons, down to the minute, seems entirely ridiculous. But, then again, it almost certainly seemed just as ridiculous in the late 1990s. What on earth could have led anyone to believe that experts employed by the Department for Education could stipulate the right length of a lesson, and the right focus of skills, to suit every class in the land?

What difference has the literacy hour made? 

By contrast, nearly a quarter of a century later, it has become the norm for the government to dictate the detail of the curriculum, although now it’s alongside even more foundation subjects and ever greater expectations of outcomes. 

And there’s no doubting the fact that the strategies of the late 1990s - both numeracy and literacy - have had an impact on the timetabling of those subjects. In a poll I carried out last week, around 95 per cent of primaries now focus their mornings every day on those two subjects.

Arguably, the focus on those two subjects has led to a clear increase in attainment in English and maths in primary schools, as Sats results rose year on year. And rightly they should, as ever greater allocations of time were given over to the subjects. But then a look at international data like Pisa (the Programme for International Student Assessment) suggests barely any real improvement at all.

So here we are, 25 years on, with English and maths dominating primary schools, foundation subjects squeezed, and what have we got to show for it? 

I suppose at least we should be grateful for the fact that we’re allowed to choose for ourselves how long each part of our lessons should last. For now, at least.

Michael Tidd is headteacher at East Preston Junior School in West Sussex. He tweets @MichaelT1979