Nothing lost by not sending a letter. Most schools advertise their support staff vacancies in the local papers, you might save them from having to place that ad! If you send a CV make sure you emphasise anything you have done with children eg helping out at Sunday school, scouts, sports club etc. Be aware that most technician/ curriculum assistant jobs are term time only, possibly reduced hours and the wages pro rata (ie rubbish!). Expect a wage after pro rata to be less than 15K, possibly even below 10K depending on where you live and hours.