Ministers may have to wait until almost 2007 before they know if they can meet their target of recruiting another 3,000 teachers - the year in which the partnership agreement between Labour and the Liberal Democrats is supposed to deliver on the policy.
This emerged following publication of the first teacher census since 1998, and the first to have collated the information electronically.
Despite political and media scepticism, the Scottish Executive remains bullish that it will achieve its target. But, with the length of time required to boost teacher numbers, any big increase will only come through in 2005 when this year's student intake emerges from one-year training courses.
They will then have to complete their induction successfully before taking up permanent posts and appearing in the September 2006 census - results of which will not be reported until the following year.
Executive officials believe they are on course to recruit the extra 3,000 teachers. This is despite a drop of 730 teachers in the September 2003 census.
The complex planning involved in predicting teacher supply, taking account of factors such as pupil numbers, the age profile of the profession, numbers of returners and wastage rates, pointed to the need for 10,000 new students enrolling on the one-year postgraduate certificate of education (PGCE) and the four-year bachelor of education (BEd) courses in the four years from 2003-07.
More than 6,000 of these would be needed anyway, leaving the remainder to meet the Executive's target.
Officials say they will maintain a close eye on developments. The teacher workforce planning exercise, carried out each autumn, will provide early evidence if there is any slowdown in recruitment that requires further action.
The additional 3,000 staff are required to reduce class sizes in P1 to 25 and S1-S2 English and maths classes to 20, as well as to meet ministerial commitments to hire extra physical education, music and drama teachers and increase the number of "those working with young people who have particular barriers to their learning".
But political opponents were quick to seize on the drop in numbers to suggest the Executive was in danger of being blown off course. Brian Adam, the SNP's deputy education spokesperson, pointed to "the underlying problem" of the large proportion of teachers reaching retirement with not enough entering the profession to replace them.
Lord James Douglas-Hamilton, the Tories' spokesman, suggested central planning to deliver ministerial targets would not work, and that teachers and parents had to be freed from Government controls.
The Executive points out that the census was conducted in September last year, only four months after the target had been enshrined in the agreement between the parties in the ruling Labour and Liberal Democrat coalition.
Despite the short notice, they had been able to add another 200 students to the PGCE primary course at the start of the last academic session.
The census revealed a drop of 818 teachers in primary, secondary and special schools, making a total of 49,230 teachers. But there were also 1,733 teachers in the pre-school sector, bringing the total to 50,963 - 730 fewer than in 2002.
In addition, 1,987 teachers were employed by education authorities as visiting specialist and peripatetic teachers. They are not involved, however, in the calculations to deliver the extra 3,000 teachers.
The Executive meanwhile is to look more closely at the reasons for the growing dearth of men in teaching - especially young men. The proportion of males fell from 30 per cent in 1996 to 26 per cent in 2003. Fewer than 1 per cent of primary teachers and just over 3 per cent of secondary teachers are men in their 20s.
While the profession will continue to be promoted, officials want research into factors that may be turning men off teaching, perhaps even those who had applied for teacher training.
"We need to understand much more," one official said. "But we don't kid ourselves that overnight we can turn round what are probably very powerful forces in Scottish society acting against the attraction of men into professions such as teaching."