Phenotypic plasticity can be important for local adaptation, since it enables individuals to survive in a novel environment until genetic changes have been accumulated by genetic accommodation. By analyzing the relationship between development rate and growth rate, it can be determined if plasticity in life history traits is caused by changed physiology or behaviour. We extended this to examine if plasticity had been aiding local adaptation, by investigating if the plastic response had been fixed in locally adapted populations. Tadpoles from island populations of Rana temporaria, locally adapted to different pool drying regimes, were monitored in a common garden. Individual differences in development rate were caused by different foraging efficiency. However, developmental plasticity was physiologically mediated by trading off growth against development rate. Surprisingly, plasticity has not aided local adaptation to time-stressed environments, since local adaptation was not caused by genetic assimilation but on selection on the standing genetic variation in development time.