NB: borrowed heavily from the work of Abrahams, Millar, Reiss and Osborne.
There are a lot of reasons to do practical work in science lessons. Lighting a Bunsen burner is a right of passage. 'Blowing stuff up' is something that primary students look forward to when they come to secondary school. But does it do what we think it does? Does the way that we teach it have the effect we would like?
(Spoiler: not everything, but that doesn't mean we should give up on it).
Does it promote interest and motivation towards science? It makes lessons more 'fun', but doesn't do a lot to promote motivation towards science long term. My anecdotal evidence would agree with that. I did mathematical physics at university because I really didn't like practical work. I didn't like it because I already knew what I was going to find out from it. When I got to university the practical physics lecturers were dismayed - practical physics is the 'truth' (for want of a better word) and the mathematical things that describe it are contrived by humans. Oh. I find that students often long for the 'fun' of doing a practical and when there are not many sometimes can be turned off by the lack of the anticipated excitement.
Does practical work help to develop skills? It depends what is meant by skill. If by skill it is meant 'manipulative skill' of using the equipment, then yes it does make a difference. If you are learning to do something or use something then doing it helps. The real challenge here will be to the GCSE examiners in writing papers that test this. If we are talking about transferable problem solving skills or creativity then practical work does not seem to have an impact here either.
Does it enhance the understanding of scientific ideas? Not very well. The use of practical does not improve the performance of students in pen and paper tests. Although students carry out investigations, following instructions well and even making appropriate observations, they often cannot link the practical to the subject being learned. There have been a lot of projects trying to improve teaching using practical work. http://www.gettingpractical.org.uk But of course it is extremely difficult to change the practice of science teachers and projects like this haven't had a great impact.
Does practical work develop understanding of the nature of science? Hopefully with the new GCSE it can, but prior to that we students were looking for the 'right' answer and this isn't how science (should) works. We often teach about experiments and theory in such a way as to confuse students about the interplay between the two. Practical work in school is not representative of the way that scientists really work.
So should we bin practicals?
No. We should get better at them.
Firstly, we are required to do practical work at GCSE and A-level. As educators we would be in trouble if we did not give our students the opportunity to do the required and core practicals. This is to ensure that students do have the manipulative skills that practical work does teach. Universities are keen that students arrive being able to use equipment and the best way to teach this is through practical.
Secondly, we should be allowing students to experience scientific phenomena for themselves. Experimental work is an important feature of science, after all observations are what we are trying to explain. However, the science is often counter intuitive and therefore you cannot understand everything from observation. The teacher is needed as a mediator.
Thirdly, we should use practical work to help students understand enquiry. However, again this is not something we do well. How many of us have the time to allow students to work through an entire investigation and analysis of the results? Before an investigation it is important that students have a good understanding of the question they are asking and are able to select from the different types of enquiry which is the most appropriate. How many teachers know what the five types of enquiry are? (Other than fair testing).
And finally, we can do better at teaching students about science phenomena through practical work. But we have to be clear about our expectations for the outcomes for students, both from the practical work and what they can do and apply afterwards, particularly at secondary level.
Further reading (may need to be an ASE member to access all of these).
May 2015 School Science Review (practical work theme): http://www.ase.org.uk/journals/school-science-review/2015/05/357/
September 2009 School Science Review, Millar and Abrahams, Making Practical Work More Effective: Practical work: making it more effective (warning may download directly)
Abrahams and Reiss Effective Practical Science (Bloomsbury) Amazon Enhancing Practical Science
Abrahams: Practical Work in Secondary Science (bloomsbury) Amazon Practical Work in Secondary Science
December 2010 School Science Review, untangling what teachers mean by the motivational value of practical work. Untangling what teachers mean by the motivational value of practical work (warning may download directly)
Article about the 5 types of enquiry: IT'S NOT FAIR - The Association for Science Education (warning may download directly)
Education in Chemistry, Practical Work a New Opportunity: https://eic.rsc.org/cpd/practical-science/2000009.article
Getting Practical: http://www.gettingpractical.org.uk