Via video link, David told us about how he started out as an IT engineer connecting computer hardware, then programming firing systems on tanks, before more recently managing an educational software company.
Lester, who qualified as a mechanical engineer, spoke about designing energy efficient air conditioning systems in large buildings.
The children enjoyed his science demonstrations: a piece of paper lifted in the air; a balloon suspended over a fan; a dvd floating on a cushion of air.
Interlocking cardboard boxes made their fun debut in the STEM area. Once the towers were knocked down, a few giraffes were built. After the giraffes lost a few pieces, a cardboard house appeared. After one of its walls was accidentally demolished, an impressive STEM castle took its place. -mjp