Numbers are formatted as text in the exported file
This is a known behavior and it's due to the numbers in 4Matrix being stored as a string. This is because we would generally hide or remove pupils from calculations when filters are applied in order to prevent them from registering as a 0 value.
The workaround in MS Excel is to copy the exported sheet and paste into a new sheet or workbook using the Paste Special 'As Values' option. This will then allow you to select the numeric cells and use the small exclamation mark (which appears in the top left cell of the selection) and choose to 'Convert to Number'.