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    chaohz主页 >> 文章 >> 教学文章 >> 浏览信息《“短除法”是不宜删去的核心技能》

    教学文章 | 评论(2) | 阅读(1640)
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    星期四   晴天 
    主题 “短除法”是不宜删去的核心技能

    “短除法”是不宜删去的核心技能

     

     

     

    江苏省江阴市夏港实验小学    巢洪政  214442

     

     

     

    对于新课标教材删去“短除法”的做法,本人一直是持保留意见的,因为,个人认为“短除法”是保证求两个数的最大公因数和最小公倍数简捷正确的核心技能,是属于不宜删去的教学内容。

     

     

     

    我曾经两次教学苏教版五年级下册中“公倍数和公因数”的教材,教学的实践就可以明确地回答这个问题。第一次由于是初次教学新教材,所以我严格按照教材的要求和教学用书的指导进行教学,让学生用例举法求两个数的最大公因数和最小公倍数,这样教学在起初的练习中效果也还不错,特别是对于数据不是很大的两个数,学生求它们的最大公因数和最小公倍数时的正确率还是比较高的。但是,过了一段时间后,让学生仍然用这样的方法求最大公因数和最小公倍数时,学生的错误就明显增加了,特别是有些口算能力差的学生,几乎很难求对两个数的最大公因数和最小公倍数,遇到两个较大数时,情况更加糟糕,到后来还影响了异分母分数加减法和约分的教学效果。分析其中的原因,主要的问题在于例举法对口算的要求比较高,口算的次数也较多,如果有一步口算错误,往往就导致整个求解过程的错误,而现在学生的口算能力下降也是不争的事实,所以,例举法的错误率当然就高了。而“短除法”却不同,学生只要将两个数列出,按部就班地用素数2357……作为除数逐个试除,在得到的商互质后,就很容易得出两个数的最大公因数和最小公倍数,这样操作性强,简捷而正确率高的方法当然受到了师生的欢迎了。所以,在第二次教学这部分内容时,我就毫不犹豫地从例举法引入最大公因数和最小公倍数的知识,重点教学“短除法”求最大公因数和最小公倍数,果然在后面的练习中,学生的正确率明显上升了。

     

     

     

    这样看来,“短除法”属于教学这部分内容的核心技能,对正确求出两个数最大公因数和最小公倍数起有关键作用,所以是不宜删去的,许多老师的教学实践研究也都证明了这样的结论。从智育心理学的角度分析,要使学生牢固掌握求两个数的最大公因数和最小公倍数的知识,必须将求最大公因数和最小公倍数的陈述性知识转化为程序性知识,才能增强可操作性,提高正确率,用“短除法”计算正好起到了这样的作用,而例举法则没有这样的优势,所以学生记不牢,易错误。有些老师认为这样的知识是一种机械的操作,这样的知识价值不高,其实是一种完全错误的认识,这与新课改轻视技能教学的理念有关,这样的理念已经导致小学生计算能力下降已经为大家所公认,其实,帮助学生掌握必要的计算技能也数学教学的重要目标之一,对于这样的核心技能尤其如此。这也就难怪至今这么多老师仍然采用、有许多同学喜欢“短除法”的原因所在。

     

     

     

    由于正确求两个数的最大公因数和最小公倍数还是后面约分、通分和分数加减计算等知识的基础,是必须学好的知识,所以,我个人呼吁在下一轮教材的修订中应该对现行教材进行必要的修改,补充分解质因数的知识后,仍然教学用“短除法”求两个数的最大公因数和最小公倍数。

     

     

     

    因为“短除法”是不宜删去的核心技能!

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    chaohz 发表于:2011-4-7 7:59:04

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