Lesson objectives help students to focus their efforts and to gauge their progress.  Writing lesson objectives also helps teachers to stay focused and to measure how well students are learning.  "A well-written objective statement provides a clear picture of the outcome or performance you expect as a result of the lesson. It should be specific, concise, and, most importantly, observable or measurable." (from www.glencoe.com/sec/teachingtoday/downloads/pdf/objective_statements.pdf) 

When writing a learner objective, think in terms of completing the sentence "students will be able to...".  Then choose one of the following verbs and you have a great start to an objective: 

recall, identify, recognize, acquire, distinguish, state, define, name, list, label, reproduce, order, select, illustrate, represent, explain, classify, apply, sequence, carry out, solve, prepare, operate, plan, explain, demonstrate, instruct, use, perform, employ, solve, compare, explore, distinguish, determine, examine, write, plan, specify, produce, organize, design, build, combine, summarize, restate, argue, discuss, generalize, produce, evaluate, assess, test, judge, rank, measure, appraise, select, assess, check, determine, support, defend, participate, cooperate, help, adjust, measure, perform, operate, use, or move.

Avoid using verbs such as know, understand, learn, familiarize, gain, knowledge of, comprehend, study, cover, learn, appreciate, become acquainted with, realize, or be aware.  These are very hard to measure.