Chinese sentence when only object is mentioned
Grammar books seem to split the 是……的 grammar construct into a whole bunch of cases (and here and here) using jargon like distinguishing words.  I prefer to simplify, and think about this grammar construct as meaning:

X 是 Y 的
X (noun phrase) has the property Y (adjective phrase)

It's perhaps linguistically imprecise, but all we're really doing is applying some kind of adjective (described by Y) to some kind of noun (given by X).
So:

这是真的。
This has the property of being true.
This is true.


那辆车是红色的。
That car has the property of being red.
That car is red.


这个消息是昨天发布的。
This news has the property of being released yesterday.
This news was released yesterday.


我们是2011年认识的。
We have the property of having met in 2011.
We met in 2011.


我是坐飞机来的。
I have the property of coming by plane.
I'm coming by plane.

And finally...

他的成绩一直是我们班最好的。
His grades always have the property of being the best in our class.
His grades are always the best in our class.