Some authorities/areas operate an opt-in system, while others (such as Buckinghamshire) operate an opt-out system where all pupils are entered unless parents decide to opt out. In the North Yorkshire, Harrogate/York area, children are only required to sit two tests: Verbal and Non-Verbal Reasoning. Independent schools in England generally select children at the age of 13, using a common set of papers known as the Common Entrance Examination About ten do select at eleven; using papers in English, Mathematics and Science. These also have the Common entrance exam name. Scoring England has 164 grammar schools, 85% of which are academies at liberty to set their own individual admissions criteria including the type of entrance tests they set and what weighting is given to each one. Schools frequently form consortia to set a common test or get the local authority to administer it but despite this there might be about 70 different 11+ tests set each year across the country meaning it is no longer possible to talk about the eleven plus test as a single entity. The actual marks from these tests, referred to as raw marks, are never disclosed, instead parents are given Standard Age Scores (SAS). A standard score shows how well the individual has performed relative to the mean (average) score for the population although the term population is open to interpretation. GL Assessment, who set the majority of 11+ tests, say it should be, "a very large, representative sample of students usually across the UK"; however, grammar schools may standardise their tests against just those children who apply to them in a given year, as this enables them to match supply to demand. Test results follow a normal distribution resulting in the familiar bell curve which reliably predicts how many test takers gain each different score. For example, only 15.866% score more than one standard deviation above the mean (+1σ generally represented as 115 SAS) as can be seen by adding up the proportions in this graph based on the original provided by M. W. Toews). By standardising on just the cohort of applicants, a school with for example, 100 places which regularly gets 800 applications can set a minimum pass mark of 115 which selects approximately 127 applicants filling all of the places and leaving about 27 on the waiting list. The downside of this local standardisation, as it has been called, is parents are