GEANT4 simulations of the processes affecting the transport and collection of optical photons generated inside a scintillation detector were carried out, with the aim to complement the educational material offered by textbooks to third-year physics undergraduates. Two typical situations were considered: a long scintillator strip with and without a wavelength shifter fibre embedded. Various aspects were studied, including the reflection of photons on realistic coating interfaces, their absorption in the bulk material and the effect of the wavelength shifter fibres. Examples of experimental results obtained with such a detector setup, as actually obtained within a third-year laboratory activity, are also included. (Contains 1 table and 9 figures.)