For instance, suppose that we have limited resources for early childhood education, and we can only provide a certain program to a handful of at-risk children. Perhaps 1000 families apply when the program has a capacity of 500. How do we decide who to let in? Often we will use a lottery, specifically because it's viewed as the fairest and most ethical solution! In this case, my argument is simply that we should keep better data on the randomization, and record outcomes for both lottery winners and losers. The same holds for lotteries at oversubscribed charter schools, or assigning kids to kindergarten teachers. As Kevin Carey points out: "Given that teacher assignment often unfairly reflects parental pressure, periodic random assignment could be a net increase in fairness for students."
In most instances, you can reframe randomization in education as "allocating scarce resources in a way that doesn't reward parental connections", or "making sure that a program works before we open it to everybody", and it sounds great from an ethical perspective. It will be very sad if knee-jerk aversion to experiments keeps us in the dark about what's really effective in education.