Which lesson am I doing again?

Today at school.......
couldn't even decide which lesson I was meant to be teaching. Year 3 come into the room for their lesson. I sit them all down and then launch into 10 minutes of really good recapping and expansion on the subject of databases after we had our first lesson on it last week.
They're doing really well, remembering that a database is used to store and organise information, what a record is, what a field is and I'm really on a roll.
Then I send one of the girls to get the ICT books from their classroom.
When she comes back, she quietly tells me that it's meant to be a research lesson on the Romans and the second database lesson is meant to be later in the week.
Ooops and arse.