阅读 Passage 1,完成小题.
Passage 1
Today'sadults grew up in schools designed to sort us into the various segments of oursocial and economic system. Theamount of time available to learn was fixed: one year per grade. The amount learnedby the end of that time was free to vary:?some of us learned a great deal; some, very little. As weadvanced through the grades, those who had learned a great deal in previousgrades continued to build on those foundations. Those who had failed to masterthe early prerequisites within the allotted time failed to learn that whichfollowed. After 12 or 13 years of cumulative treatment of this kind, we were,in effect, spread along an achievement continuumthat was ultimately reflected in each student's rank in class upon graduation.
?Fromthe very earliest grades, some students learned a great deal very quickly andconsistently scored high on assessments. The emotional effect of this was tohelp them to see themselves as capable learners, and so these students becameincreasingly confident in school. That confidence gave them the inner emotionalstrength to take the risk of striving for more success because they believed thatsuccess was within their reach. Driven forward by this optimism, these studentscontinued to try hard, and that effort continued to result in success for them.They became the academic and emotional winners. Notice that the trigger fortheir emotional strength and their learning success was their perception oftheir success on formal and informal assessments.
?Butthere were other students who didn’t fare so well. They scored very low ontests, beginning in the earliest grades. The emotional effect was to cause themto question their own capabilities as learners. They began to lose confidence,which, in turn, deprived them of the emotional reserves needed to continue totake risks. As their motivation warned, of course, their performance?plummeted.These students embarked on what they believed to be an irreversible slide towardinevitable failure and lost hope. Once again, the emotional trigger for theirdecision not to try was their perception of their performance on assessments.
?Consider the reality—indeed, the paradox of— the schools in whichwe were reared.?If some students worked hard and learneda lot, that was a positive result, and they would finish high in the rankorder. But if some students gave up in hopeless failure, that was an acceptableresult, too, because they would occupy places very low in the rank order. Theirachievement results fed into the implicit mission of schools: the greater thespread of achievement among students, the more it reinforced the rank order.This is why, if some students gave up and stopped trying (even dropped out of school),that was regarded as the student's problem, not the teacher's or the school's.
??Onceagain, please notice who is using test results to decide whether to strive forexcellence or give up in hopelessness. The "data-based decisionmakers" in this process are students themselves. Students are decidingwhether success is within or beyond reach, whether the learning is worth the requiredeffort, and so whether to try or not. The critical emotions underpinning thedecision making process include anxiety, fear of failure, uncertainty, andunwillingness to take risks-all triggered by students ' perceptions of theirown capabilities as reflected in assessment results.
?Some students responded to the demands of suchenvironments by working hard and learning a great deal. Others controlled theiranxiety by giving up and not caring. The result for them is exactly theopposite of the one society wants. Instead of leaving no child behind, thesepractices, in effect, drove down the achievement of at least as many studentsas they successfully elevated. And the evidence suggests that the downsidevictims are more frequently members of particular socioeconomic and ethnicminorities.

What has made students spread along an achievement continuum according to the passage?

A.The allotted time to learn.
B.Social and economic system.
C.The early prerequisites students mastered.
D.Performance on formal and informal assessments.