Learn Finnish: Opettaja asettaa pöydät peräkkäin. - The teacher places the tables one after the other.

It is built from the noun perä (rear, back) and the mutual arrangement suffix -kkäin. While it literally suggests being placed "rear-to-rear" or "back-to-back," it is the standard way to say things are placed "one after the other," "in a line," or "consecutively."

Can peräkkäin be used for things other than physical objects like tables?

Yes, it is very commonly used for time and events! For example, if you do something "three days in a row," you would say kolme päivää peräkkäin.

Why is the object pöydät in the standard plural form (t-plural) instead of the partitive plural pöytiä?

Using the t-plural pöydät makes this a "total object." It tells us that the teacher is placing all of the specific tables in a completed action. If the sentence used the partitive plural pöytiä, it would mean the teacher is placing an indefinite number of tables (just "some tables") or that the placing process is currently ongoing.

What is the difference between using asettaa and the more common verb laittaa here?

Asettaa means "to place," "to set," or "to position." It is slightly more formal than laittaa (to put) and implies a deliberate, careful arrangement, which makes perfect sense when lining tables up in a specific pattern.