The annual tables of school examination results should always be approached with caution.

Not only can such lists never properly reflect the diversity of schools and communities in Scotland; they also do not take into account other important factors such as school size, teaching ability, or how much help pupils are given by parents or tutors.

However, even such a blunt instrument can contain some important signposts for parents, teachers and councils, and this year's tables are no exception. At the top yet again is East Renfrewshire. In addition, schools in the local authority area have shown significant improvement on last year, when 32% of pupils achieved five Highers or more; this year that figure has risen to 39%.

Clearly, the demographics in East Renfrewshire work in the schools' favour. Not only will people looking for a good school move there (if they can afford to); parents in the area are also more likely to place a high value on education and therefore their children are likely to do so as well.

Nevertheless, it would be churlish to deny the schools in East Renfrewshire the credit they deserve because what they are doing is delivering for pupils. That is in part because of attention to the detail of pupils' academic lives. It is also because they challenge pupils to achieve.

Of course, in East Renfrewshire, such a strategy will have considerable parental support, something that cannot be taken for granted in many other areas in Scotland that face the challenges of deprivation in a more direct way. Take Glasgow, for example, with the poorest performing schools. The city council is sometimes accused of using poverty as an excuse for this, but a fairer way to put it would be that poverty is not so much an excuse as a reality for many schools in the city. It is certainly the single most important factor in determining exam attainment, which is why The Herald publishes data on the proportion of pupils receiving free school meals alongside the data on exams.

However, none of this should allow Glasgow's schools to resign themselves to their place and, indeed, just like East Renfrewshire, they have shown improvement, albeit at a more modest rate. Last year, 8.2% of pupils in Glasgow schools achieved five Highers or more; this year it was 8.4% (two years ago, it was 6.8%).

Some of this improvement may well be down to the fact many Glasgow schools have begun to use some of the strategies, such as early intervention, that have yielded results in other areas. At St Thomas Aquinas Secondary in Glasgow, for example, the teachers have put greater emphasis on high expectations and study support and have seen the percentage of pupils achieving five or more Highers double in five years.

Such results may be signposts of success, but they should not blind teachers and parents to the important caveats that come with league tables. No parent should rely solely on tables when making the decision on where to send their children. But equally no school should entirely ignore the lessons the tables can hold.