A third of newly qualified teachers take longer than a year to complete their induction, according to figures released last week by the General Teaching Council for Wales.
The 2007-08 statistics also reveal that the time taken to complete statutory induction varies widely, depending on a teacher's subject, what qualification they choose to take, and whether they are primary or secondary specialists.
Induction is a one-year programme of development that all new teachers must complete to carry on teaching in a state school.
Each teacher's experience is unique, but most are required to observe other teachers, visit schools and take part in formal training.
Of the 1,264 teachers who met the standard last year, 857 finished, but the remaining 407 took longer.
Only half of all primary-trained teachers finished in a year, compared with more than 80 per cent of secondary-trained teachers.
More teachers on PGCE courses finished in a year than those on a BEd. And almost all those trained in combined science and English finished in a year, while teachers in other subjects took longer. Men generally finished faster than women.
Hayden Llewellyn, of the GTCW, said the council had written to the government recommending further research into why some teachers take longer than others.
But a government spokesperson said this week: "Teachers' careers do not all follow the same path and our induction provisions allow for flexibility. It is inevitable that NQTs may take varying lengths of time to complete their induction."