Students (especially the younger ones) need more instructions (guidance) than you would expect. Things that might seem obvious for a (more) experienced user (pressing a button or tab, clicking on an item to change its appearance or characteristics) are often not clear to new users. Many of the labs and apps listed in the Go-Lab repository (for instance all the PhET labs) don’t contain instructions for use. This means that users have to find out for themselves which elements can be manipulated and what they should do and in which order. This leads to trial and error behaviour and sometimes to frustration.
Put in the text explicit statements about what students are expected to do. For instance: “Now you have reached the end of the Orientation phase, press the tab “Conceptualisation” to go to the next phase” or “Click on the tube when you want to change the characteristics of the fluent or from the ball in the tube. Then use the sliders in the top of the window to actually change the characteristics”.