Forty minute periods thwart investigation. I found period scheduling far more constraining than self-contained classrooms, though I spent comparable time in each. With periods we rarely seemed to have the time we needed to reflect and question. I also noted a tendency for students to wait things out if they didn't enjoy or understand an activity. They knew the period would finish whether or not they did.
Students are more intrigued by experiencing than by understanding.
One strategy I tried was to have students predict outcomes and vote on these before experimenting. When teaching another concept, I repeated the strategy by asking students to predict how water would drain from a bottle if we poked a line of holes down its side. Discussion and investigation resumed but without much productive inquiry. With a second class I changed the approach by focusing on how we could determine water pressure using tools and poking holes and they went at it with abandon. I now think it's the activity, not the strategy, that made the difference.