Estate agents boards for any purpose are an eye sore - for sale, to let or advertising a school fair. In this modern age of social media and the internet, these boards are a relic of the past.
It has been said by others that using these boards for advertising school fair and raising money is a lazy way of fundraising - you do not have to do anything except agree for the board to be nailed to your gate - no effort required from the school, parent or the child !