Each lesson that is delivered will include a key objective that the teacher would like all pupils to achieve. Each objective will include a command word which is taken from Bloom's taxonomy. Bloom's taxonomy is a hierarchy of skills which categorises tasks by the level of demand that is placed upon the learner.
For example, the graphic below shows that tasks which require pupils to 'describe' or 'identify' are taken from the 'Knowledge' category and place a relatively low level of demand upon pupils. Tasks of this nature would typically be encountered at the beginning of a new topic when depth of knowledge is limited. Tasks which require pupils to 'Assess' or 'Evaluate' appear in the 'Evaluation' category are more demanding and would appear far later in the learning journey.
Typically, as pupils are introduced to new topics, it is expected that they would work their way up the Bloom's pyramid with tasks increasing in demand as subject content becomes more familiar and pupils are able to demonstrate a secure understanding.