What do you know about the history of these students? How long have they been learning Spanish and how many lessons did they have per week/fortnight? How have the predicted grades been arrived at? If they are FFT I would take them with a pinch of salt. Have they all come from one class? Are they feeling resentful/ uncertain at having a new teacher? If they are D/C borderline they won't need to be able to conjugate verbs in 3 tenses. So you would be needlessly creating a rod for them to beat your back. Why have this small group chosen to study Spanish? How well were they taught in the past? Their lack of knowledge could be the result of poor past experiences. However if they have chosen to study Spanish it must be for a reason. I would try to find out their motivation and orientate what I taught them towards that. I am sure that you would get much further with them if you make the lessons enjoyable, rather than antagonising them with grannar exercises. I have had 'impossible' classes and colleagues have advised me to meet them at the door and try to make yourself look pleased to see them, try to share a joke with them, lighten up and think of what they are enabling you to earn.