Sure it's meaningful—it's unclear, however, whether this is a single-yard experiment with replacement (and, we assume, a negative control, since it's possible some boys would be brought to the yard simply by the weather or the conditions inside) or a two-yard competitive boy-bringing experiment. Given the overwhelming preference shown, it seems probable that both experiments would produce similar results, but for completeness, the authors should consider running both and comparing the results.

In the case of the single-yard experiment, multiple trials should also be run with varying milkshake orders, to avoid satiation effects.