Whoever came up with the phrase 'Your schooldays are the best days of your life' was obviously lying - kids, your schooldays are definitely not the best days of your life.

However, some of the students at the Walter Reed Middle School in Hollywood, California may have thought differently the other day, when Lady Gaga walked into their classroom to act as their substitute teacher.

Gaga was filming an ad for her new partnership with stationery company Staples, to promote public education in the USA, although none of the ad was scripted.

Instead, the megastar just engaged and chatted with the kids, sitting in a circle 'to discuss their hopes and dreams'. As you do.

Watch it below: