If you are a teenager, certainly not 8:30 on a Monday morning. The teenage tendency to go to bed late and attempt to sleep in each morning is not just a product of laziness and/or rebellion, but a result of natural shifts in circadian rhythms for most chronotypes. Carrell et al. (2011) found that delaying the start of school by 50 minutes has a significant impact on academic achievement. Wahlstrom et al. (2014) found similar results with an 80-minute delay and extended their study beyond learning to student-involved traffic accidents, which decreased by 70% when the delay was introduced. This suggests that the battle with adolescent sleepiness is real and that trying to teach out of sync with our students’ circadian rhythms is a losing battle.

The ongoing debate about the best age for a child to start pre-school and then transition to formal learning is also instructive here. Although school systems have specific age requirements, educational researchers talk in terms of school readiness rather than chronological age. Readiness includes independence, social-emotional stamina, the ability to communicate, and brain structures developed enough to deal with the learning (Stipek, 2002). This brings to prominence the variability in the pace at which children develop these skills. This variability does not end with pre-school and it seems clear from this that not all brains are best served by the lockstep, age-based progression imposed by formal education.

As any teacher asked to teach a heavy dollop of grammar after lunch on the last day of the school week knows, time of day can also have a strong influence on students’ readiness to learn. Circadian rhythms have their influence here, too, with most people experiencing a daily peak of energy and attentiveness in the morning, followed by a trough around the middle of the day and a partial recovery in late afternoon (Pink, 2018). Day of the week also makes a difference with attention peaking on a Monday and heading downhill as the week progresses (Burger et al., 2018). No great surprise there.

Looking specifically at language learning, there is strong evidence both from L1 and L2 research that aspects of a language are acquired in a particular order, which is largely impervious to the order in which we try to teach them. In English, plural -s tends to be acquired before third person singular -s, and progressive -ing before past tense -ed. This finding is of most use to curriculum planners and textbook writers, but it does lend weight to the argument that at least part of our teaching should focus on the communication of meaning rather than the production of specific language forms at a certain time.

There is a lot of folk wisdom, and a certain amount of research, behind the idea of “a critical period” for language learning, a time when it is relatively easy to learn a language, followed by a cut-off after which it becomes much more difficult. Lennenberg’s Critical Period Hypothesis (1967) suggested that, for L1 acquisition, the brain is genetically programmed to acquire language only within a specific, biologically-determined time window (from around age 2 to puberty). Lennenberg drew on evidence from children deprived of exposure to language until their mid-teens who never managed to master syntax or grammar. More recent research into brain plasticity across the lifespan has shown that one is never “too old” to learn a language, but that adults use different neural pathways than children when learning a language and benefit from a different approach to learning.

Nowadays, we speak in terms of sensitive, rather than critical, periods for different aspects of language learning: birth to 12 months for phonology, birth to 17 or 18 years for morphosyntax, and throughout the lifespan for semantics (Friederici & Chomsky, 2017). The emphasis here is less on “learn it now or never,” than it is on the ease with which each aspect of a language can be learnt.