I will put this on the Mathematics subject forum as well but would be interested to hear views from the wider community since Mathematics is a core subject that everyone should be concerned about. I am a private Maths tutor, although I have worked in schools and colleges in the past, and have come across a number of otherwise bright students from 13 to 16 years of age, that seem to struggle with basic arithmetic and fractions e.g. 5 x 20, 2/9, etc. They have learned these skills in the past but have then used calculators ever since, so have then forgotten them. Manipulation of fractions in particular is useful skill for the GCSE exams, both Foundation and Higher, because it is often used in rearranging algebraic equations. I personally think that calculators should be more controlled in mathematics lessons and used only in those situations where to do otherwise would be needlessly tedious and distracting from the problem at hand. I won't go into too much detail but any Maths teacher will be identify those situations where a calculator is needed and when it is not. Quite often exercises can be produced or found where the numbers come out 'nicely' provided students look for shortcuts that make calculations easier like cancelling down fractions or 'doubling-and-halfing' e.g. 5 x 16 = 10 x 8 = 80, etc). And for those occasions where calculators are useful, students need to be made aware of how to use them properly e.g. when to use brackets, using the result of the previous calculation in the next calculation, checking whether answers are reasonable, or not, by using estimation, etc.