Between 70 and 80 per cent of 14-year-olds in Wales are expected to reach level 5 or better in maths, science and English or Welsh by 2002. But, without faster progress, only the Welsh language target will be met, says Miss Lewis.
In her annual report, published last week, she notes that pupils' results improved last year in tests at key stages 1 and 2, and in GCSE and other public exams.
But results at key stage 3 were roughly the same. Moreover, it is at this stage that standards vary most and the percentage of unsatisfactory teaching is highest; teachers' expectations were too low and their range of teaching techniques too narrow in more than half of the lessons inspected.
This year's report finds more good work in primary schools than last year, while, in secondary and special schools, standards have only been maintained.
However, many secondaries that were performing badly five years ago have made significant progress. And teaching quality for those over 16 remains high.
Truancy remains a serious problem in secondaries: nearly half of those inspected last year had attendance levels below 90 per cnt. In a small minority, one fifth of pupils is regularly absent.
In primary schools, while overall standards of achievement remain broadly the same as last year, there is more good and very good work and a smaller gap in performance between key stage 1 and key stage 2.
Literacy and numeracy are satisfactory or better in more than 90 per cent of primaries but writing and numeracy are weaker than reading and oral work.
At secondary level, literacy is satisfactory or better in nearly 90 per cent of schools and at least satisfactory in numeracy in almost all schools. However, only one school in 10 makes sure that pupils develop and use numeracy skills across the curriculum.
Inspectors were concerned about standards in information and communications technology - unsatisfactory in about 60 per cent of secondary schools. In nearly half of schools, poor equipment makes it difficult for pupils to use ICT across the curriculum.
Poor buildings have an adverse effect in more than a half of schools, the inspectors report. Problems in primary schools include classrooms that are too small for the number of pupils, the lack of a decent school hall and poor toilet facilities.
"The Annual Report of Her Majesty's Chief Inspector of Schools in Wales 1998-99" is available from Stationery Office bookshops, price pound;13.