“… the local authority’s duty during assessment is not merely to identify the child’s needs – though that is presumably part of the process of assessing them – it is to “assess” the child’s needs. “Assessment” goes beyond mere identification of needs; it involves analysis and evaluation of the nature, extent and severity of the child’s need, a process which must go far enough to enable a pathway plan to be prepared setting out in sufficiently precise detail the “manner” in which those needs are to be met”