在笔者的教学中，除了一直在强调官方评价标准外，也一直强调写作规范，其实在词汇方面，也是有特定的规范的，可是这个规范极难把握。在作文评语当中，老师和考官也往往只用“appropriate”一词来概括。什么样的词汇是“appropriate”的？笔者个人觉得极难说清楚，有些写作教程会用“适合作者写作意图”又或“与所表达的内容自然地融为一体”来表述，但何谓“适合”和“自然”却没有进一步说明；另一方面，什么样的词汇是“inappropriate”的，通过教学实践，笔者却可以说出好几种：
1. 口语化语言或俚语
口语和书面语显然是有比较大的区别的：前者较随意，后者较正式；前者可以在语法层面犯些不影响理解的错误，后者必须按照语法规则书写；前者有时受发音规则影响，后者则不考虑音节因素。由于这些区别，口语化的语言是不适合出现在规范写作中的。
俚语也是一样，作为另一种较口语的语句，是民众在日常生活中总结出来的通俗易懂又顺口的表达。特点是地域性强，较生活化。但总体说来，俚语是一种非正式的语言，通常也只能在非正式的场合使用。例如：
【例1】 the environmental problem is pretty serious today.
修改： the environmental problem is extremely serious today.
【例2】 Should he study hard, the final exam is to become a piece of cake.
修改： Should he study hard, the final exam is not to become a problem.
【例3】 Since democracy has been acknowledged by the world, it is sort of strange to see some politicians lean on the authority.
修改： Since democracy has been acknowledged by the world, it is a little strange to see some politicians threaten the authority.
2. 行话
同学们经常犯错的另一个极端是行话。所谓行话，指的是某一特定的社会群体，由于工作上、活动上或其他目的上的共同性，在相互之间交往交流时，会创造、使用一些不同于其他社会群体的词汇、用语或符号。比如早期的军事部门，再比如现在的通信行业。我这里所说的行话并没有那么偏远，指的更多的是学生在写作学习中经常背诵一些“较难”的同义词，却没有仔细辨析这些同义词含义的区别。殊不知，很可能使用的就是只有英语国家的政府单位、商业公司、学术机构、甚至军队才会用的一些表达。当然，并不是绝对不能用这些词汇，除非不用这些专业用语就无法表达其准确含义。举一些使用行话不恰当的例子：
【例4】 The new generation is believed to commence their age by ameliorating the living conditions in economically deprived areas.
修改： The new generation is believed to start/create their age by improving/changing the living conditions in poor/less-developed areas.
【例5】 It is hard to believe that students perusing books all the time without thinking critically can actually carry out viable life goals.
修改： It is hard to believe that students reading books all the time without thinking critically can actually arrange his life properly.
【例6】 When they night came, they went out for a perambulation, but soon enough, they shrank back in discomfort, surmising that an unidentified object tried to murder them.
修改： When they night came, they went out for a walk, but soon enough, they returned in discomfort, dreading somebody in the dark who tried to kill them.
3. 过于“华丽”或“矫揉造作”的词藻
这一般是水平较高的学生为了取得25分以上的分数，想创造一些个性化语言时所犯的错误。这样的情况在教学过程中见到的不在少数。有些语言读来让笔者看到眼前一亮，但更多的情况是不但没有给笔者留下深刻的印象，反而使笔者感到华而不实。有些甚至是晦涩难懂的，读来令人非常吃力。盗用一句名言就是“a misconception frequently held by novice writers is that word choice mirrors thought: the more impenetrable the word, the more involved the ideas.” 以下也举几个例子：
【例7】 Unfortunately, the TV station in some countries does not have an appropriate classification of adult entertainment, so children may have access to those unhealthy programs.
修改： Unfortunately, the TV station in some countries does not have an appropriate classification of pornography, so children may have access to those unhealthy programs.
【例8】 One feasible solution is that the industry should be stopped and those who have more than enough cars should sell their preowned automobiles.
修改： One feasible solution is that the industry should be stopped and those who have more than enough cars should sell their used cars.
【例9】 I do believe that no country would refuse such revenue enhancers.
修改： I do believe that no country would refuse such taxes.
以上三种是托福写作教学过程中学生经常犯的在词汇选择方面的错误。其实这三个方面还可以继续展开论述（比如行话会涉及的行业用语，日常生活中的口语分类及委婉语的概念说明），且还有其他的词汇选择方面也需要注意（比如歧视用语等），但由于篇幅所限，只对以上这三类做简要说明。