我认为这个句子是错误的。从汉译倒推，要表示从1990年一来一直当教师，谓语动词应该用be: He has been a teacher since 1990. become的无论是否用完成时都不能用持续时间状语。终结性动词的现在完成时与since状语连用可以表示事件发生的频次，如never，once，three times等。如：He has written three books since 1990. I have seen him three times since 1990. 但become a teacher既不可能谈论频次,也不能持续，因此不可以接for及since时间状语。

对追问的回答

首先感谢刘老师提供大量例句说明become的现在完成时确实可以和since状语连用，让我们开阔了眼界，对since状语的用法有了更深的了解。借此机会我对since的用法作以下分析，并对刘老师提供的例句也试作分析。

我在回答此问题以前就猜想刘老师肯定会举出一系列例句表明become的现在完成时和since状语连用的例句，因此我的用词很谨慎，我用了“从汉译反推”等。但我还是忽略一个细节，即确实有时become的现在完成时可以和since状语连用。但其逻辑意义并非“自从。。。以来一直”的意思，而是“从since提示的时间点到现在这段时间之内的某个时间”的意思。因此汉译是不应翻译为“自从。。。一直。。。”。

首先我们复习一下since的词义。词典告诉我们since有两个意思：

1从过去某特定时间起一直到现在不间断地；

英文解释：from a particular time or event in the past until the present.

2在这段时间之内的某个时间。

英文解释：in that period of time.

因此当主句的谓语动词是a) 静态动词的现在完成时;b)表示长期习惯意义的现在完成时；c)动态动词的现在完成进行时；或4）现在完成时否定式，since状语是第一个意义，即从过去某特定时间一直持续到现在。这个意义的since状语可以改为for时间状语。例如：

He has lived here since 2001.

He has lived here for sixteen years.

He has been a teacher since 2001.

He has been a teacher for sixteen years.

He has gone to the library every day since he came to Yale.

He has gone to the library every day for 3 years.

He has been writing the book since 2015.

He has been writing the book for two years.

I haven’t seen him since 2015.

I haven’t seen him for 2 years.

但主句的谓语动词为终结性动词或状态转换动词时，since状语是第二个意义，即动作的终结或状态的转换发生在从过去某特定时间到现在这段时间之内的不确切的时间点/段。动词可以是一次性，也可以是重复几次的。这种情况类似于我们用this month，this week， this morning作状语表示说话时间之前发生的动作要用现在完成时。因为这段时间包括说话时在内，但动作的具体发生时间却是说话时间之前的不确切的过去，所以要用现在完成时。这个意义的since状语不能或for状语替换。例如：

He has written 3 books since 2001.

I have seen him 3 times since 2001.

Since the end of the war, over five thousand prisoners have been released.

He lost his job five years ago, but has since found other work.

He has become a different person since his wife died.

(become发生在他妻子死亡到现在这段时间之间的某个时候，具体时间不详，即不确切的过去。)

刘老师所举的例句大致可以分为三类：前两类属于since的第二种意义。在理解和翻译的时候不宜理解和翻译成“一直”。

1 发生于包含现在时间在内的一段时间之中的事件（仍属于不确切的过去）。

She has become very sophisticated since she went to live in London.

她并非一到英国就变得老道世故，而是到了之后的某个不确切时间。

I think the situation has become worse since the current government came into power. 局势变得更糟并非发生在政府更迭的当时，而是随后的某个时间。

She has become active since last term.她的变化发生在这个学期的某个时候。

2表示重复发生的意思，不是一次变化。Become与increasingly或形容词比较级连用，表示在一段时间内变化反复发生，程度逐渐增减。但这段时间是不确切的，只是现在之前。所以用现在完成时。

He's become increasingly withdrawn since his wife's death. 

The trends since the 1950s have become even more marked.

He's become a lot more domesticated since his marriage. 

3 用for时间状语表示实际持续时间。我认为以下三个例句属于说话人不谨慎而导致的笔误或口误，正如在中文报刊中我们也能找到语法错误。因为这种用法明显和become及for的意义是矛盾的。这三个句子中的become均应改为be。

In fact Barbie has become a household name for many years.

My sister has become a college student for three years.

A close friend of mine from China has become a Singapore citizen for some years.

4 for短语其实是目的状语？

My sister has become a college student for three years.

这句话或许可以作另一种解释，即for状语是目的状语，三年制大学。我妹妹上大学了，要上三年。这种解释有些勉强，因为通常表示到达、离开的趋向性动词才做这种解释。但毕竟这是一种可能的解释。

    become 是“非延续性动词”，不能跟“for + 一段时间”或者“since ...”这类时间状语连用。

   “She has become a teacher since 1990. 自从1990年以来她就一直当老师。”中的英语句子应该改为：She has been a teacher since 1990.