Psychology your class measures on itself.

• The room's ruler

  First the room guesses how far off it will be. Then every phone matches a plain line to a line with fins, by eye, with no number to read, and the matches land on the room's ruler: half the room's fins point out, half point in, and the two halves err in opposite directions. Told the lines were equal, the room matches again and is fooled again. With no fins, the same hands land on Equal. Counts only, never names; a phone that cannot judge says so and is counted apart.

  Up to 600 people

  Visual perceptionSystematic bias

  PlayingHow it plays, and how to run it
• Name the ink

  Four index cards, read out loud and timed on every phone: name the ink of coloured blocks, then of colour words printed in clashing inks; then read the words of a clashing card and of a plain one. Each card's times land on a till receipt, one notch per person, and a second strip sets each person against themselves: the words cost almost everyone time on naming, and the ink costs almost nothing on reading. The card shows on a phone only while its own clock runs. Anyone who finds the colours hard to tell apart sits those cards out and is counted, never singled out.

  Up to 600 people

  Selective attentionAutomaticityWithin-subject design

  Try itHow it plays, and how to run it

Every activity here ships with Decka — sign up free and add any of them to your library from the built-in classroom catalog.