[NB: I could write about this for hours and give you pages and pages on enrichment, but I've tried to keep it short and snappy. Possibly too short and snappy.]
At my last school, I was Enrichment co-Lead. As a school, we were quite big on the extra- and supra-curricular activities with the students. In science this ranged from year 7 who did an ecology project to achieve their bronze CREST Award, to year 10 who did a 1-day malaria workshop designed by the Francis Crick Institute. Enrichment was a big deal. There were cries of "it will increase their science capital.", "it will make them engaged in science more", "they'll do better in their exams, because it will make science real for them". Arguably the first statement isn't wrong - it will probably increase their science capital, whatever that is. The other two? ehhhhh.
Unfortunately, the outlook is rather bleak. A longitudinal study by Pallavi Amitava Banerjee (2016) found that five years after STEM enrichment programs, the "intervention group did not do any better than the
comparator" in terms of maths attainment. [I acknowledge that this isn't science, but there can be a reasonable assumption that one's science and maths grades will be similar.] On the whole, there isn't much out there that says "enrichment activities will increase attainment". Such activities might increase the chance a student completes the academic course, but it must be noted that science clubs up and down the country are stuffed with students who already like science! One of the leading factors that contributes to student attainment is student motivation - if you turn up to class on time, with the right equipment, you're gonna do better than if you bunk off or don't bring a pen. It could be argued that STEM/science enrichment leads to an increase in motivation, but it doesn't seem to. Those who are already into science enjoy the enrichment activities, and there is a general boost, but it's sadly short-lived (Singh, Granville and Dika, 2002).
Okay, what about museums? Taking kids to the Science Museum is surely going to make them love science, right? Nope. Turns out one-off trips, when insufficiently supported, have little effect on children’s long term attitudes to science. In the short-term it's not so bad, with some evidence suggesting that trips to museums do have a positive influence, but only really if they are fully and properly integrated into the curriculum. "It is not enough to simply take children to a science museum, and expect them to enjoy science." (Allan, 2012). Jarvis and Pell (2005) looked at the impact a trip to the UK National Science Centre and the Challenger Centre had on 300 children aged nine to 11. They found that immediately after the trip, there was a boost in student enthusiasm towards science, but that five months later, 62% of boys, and 72% of girls had a substantial drop in science enthusiasm [although there is usually a drop in enthusiasm towards science in kids at that age. Not sure why].
Okay, fine, what about cool science Drop Down Days, and whizzy demos? They must make students love science and therefore do better? Right? Sorry, no again. Hands-on, or interactive demos are potentially better at getting students to reassess their misconceptions, assuming the interactive demo actually works as it should [how many times have you done the V=IR practical with a class and it just hasn't worked] but the evidence that they increase engagement and attainment is fuzzy (Zimrot and Ashkenazi, 2007). The things that most strongly impact science achievement are: prior achievement; peer environment; the amount and quality of instruction; instructional time; home environment and motivation (Singh, Granville and Dika, 2002; Reynolds and Walberg, 1991; Fraser, Walberg, Welch, & Hattie, 1987). No mention of clubs. Soz. One could argue that taking a student to a museum will increase their motivation, but unfortunately it doesn't have a long-term impact. Sure, it boosts interest briefly, but in the long term, it slides on back to where it was before.
The times when demos and museum trips and the like had the biggest impact on students, either in terms of interest and engagement, or attainment, were when they were well incorporated into the SoW. When students were prepared before going on the trip, and there were follow-up activities afterward. It takes a lot to make sure a project or a trip has sufficient wraparound to be worthwhile as a specific learning opportunity. I'm not saying we should all abandon our trips and our extracurriculars and all things fun. Kids who are interested in science love science club. Kids who are tangentially interested in science like science club. A trip to a museum, or an aquarium, or a zoo can be well-embedded into the curriculum, so that it complements the learning, rather than just being "a bit of fun". I would almost be tempted to argue that, if you have the time, it is a good thing to take students to a museum or zoo or whatever, not because of any curricular learning value, but just because it is fun, and not every student will have the opportunity to otherwise. I think there is value in e.g. seeing just how tall a giraffe is, or seeing how advances in medicine have changed the equipment used in hospitals. Just don't try to shoehorn it into a SoW. It won't have the desired effect(s).
TL;DR
Science enrichment is good fun, but it doesn't have much of a lasting impact on students, either in terms of engagement or attainment unless it is fully and properly integrated into the curriculum and has pre- and post-enrichment activities. Otherwise it's just a bit of fun. Which maybe isn't a bad thing?
The Singh, Granville, and Dika paper features this horrific flow diagram thingamabob, which I'm including here for the lulz:
Allan, C., 2012. Do science demonstrations, hands-on events and visits to museums change pupils’ long term attitudes to science?. Undergraduate. The University of Hull.
Banerjee, P., 2016. Does continued participation in STEM enrichment and enhancement activities affect school maths attainment?. Oxford Review of Education, 43(1), pp.1-18.
Fraser, B., Walberg, H., Welch, W. and Hattie, J., 1987. Syntheses of educational productivity research. International Journal of Educational Research, 11(2), pp.147-252.
Reynolds, A. and Walberg, H., 1991. A structural model of science achievement. Journal of Educational Psychology, 83(1), pp.97-107.
Singh, K., Granville, M. and Dika, S., 2002. Mathematics and Science Achievement: Effects of Motivation, Interest, and Academic Engagement. The Journal of Educational Research, 95(6), pp.323-332.
Zimrot, R. and Ashkenazi, G., 2007. Interactive lecture demonstrations: a tool for exploring and enhancing conceptual change. Chem. Educ. Res. Pract., 8(2), pp.197-211.