Achievement tests can help spot problems for a subject or for an individual sturdent.  but Political minded authorities and school boards misuse the data to reward or punish schools for their scores instead of using them for improvement.  That is how the voucher scam has stolen money from educating all students to creating a system to allow the churches and the upper classes to redistribute education taxes to the privileged few or the 'good religion.  When I see more money flowing to christian schools than to moslem or hindu or native american schools, I get even angrier at the perversion of christianity by these authoritarian hypocrites who ignore the basic principles of Jesus' alleged words in the bible.  The zealots keep citing old testament laws to justify the anger and prejudices of xenophobia. 
They ignore the Beatitudes, or the lesson of the Samaritan helping a stranger or forgiveness of the Prodigal son, or the healing of the sick, or the non judgement of women who err.