Learn Hardcore Russian: Иногда мне мешает лень делать домашнее задание. - Sometimes laziness prevents me from doing my homework.

You could also say Иногда лень мешает мне делать домашнее задание, and it would be correct, just a slightly different word order (a bit more neutral or textbook-like).

Я мешаю would mean I am in someone’s way / I disturb someone, which is a very different meaning.

Why is it мне (dative) and not меня (accusative/genitive)?

The verb мешать in the sense of to disturb, to get in the way, to hinder normally takes the dative case for the person affected:

Мне мешает музыка. – The music bothers me / The music is in my way.
Ему мешает шум. – The noise bothers him.

So in our sentence:

мне (dative) = to me / for me
The idea is: To me, laziness is an obstacle (to doing my homework).

Меня мешает… is ungrammatical in this meaning. With мешать + accusative you would get the other meaning of the verb (to mix, to stir), for example:

Мешать суп – to stir the soup.

What exactly does мешает mean here, and what other meanings does мешать have?

Here мешать means “to interfere, to disturb, to get in the way, to prevent.”

Common uses in this sense:

Тишина мне не мешает. – Silence doesn’t bother me.
Ничто не мешает нам уйти. – Nothing prevents us from leaving.

But мешать also has another very common meaning: “to mix, to stir.”

Мешать сахар в чае. – To stir sugar in tea.
Мешать краски. – To mix paints.

Context and the case you see after it (dative vs accusative / object) tell you which meaning is intended.

What is лень exactly? Is it an adjective, a noun, or something special?

Лень is a feminine noun meaning “laziness.”

It’s feminine, singular: эта лень (this laziness).
It often appears in an almost “fixed” pattern with the dative of a person:
- Мне лень вставать. – I’m too lazy to get up.
- Ему лень учиться. – He can’t be bothered to study.

In your sentence, it’s part of a slightly expanded structure:

мне мешает лень делать домашнее задание
my laziness to do homework gets in my way

So лень is the thing that is causing the problem.

Why is it делать and not делаю or чтобы делать?

Russian uses the infinitive after words like лень, хотеть, надо, можно to express what action is involved:

Мне лень делать домашнее задание. – I’m too lazy to do my homework.
Я хочу делать домашнее задание. – I want to do my homework.

So:

лень делать домашнее задание = laziness to do homework / being too lazy to do homework

Using делаю (I do / I am doing) would change the structure completely and would be ungrammatical here. Russian does not need a word like to or in order to / чтобы in this pattern; the bare infinitive is enough.

Чтобы делать would show purpose (in order to do), which is not what’s happening here.

Could we say сделать домашнее задание instead of делать домашнее задание? What’s the difference?

Yes, you can say both, but the nuance changes because of aspect:

делать (imperfective) – focuses on the process or general activity:
- мне мешает лень делать домашнее задание
  → laziness stops me from doing my homework in general, from engaging in the activity.
сделать (perfective) – focuses on the completion / result:
- мне мешает лень сделать домашнее задание
  → laziness stops me from getting my homework done (from finishing it).

In everyday speech, делать домашнее задание is more common when you mean the general activity of doing homework.

What’s the difference between домашнее задание, домашние задания, and домашняя работа?

домашнее задание (neuter singular) – “homework assignment.”
Very common and neutral. Often refers to one set of homework for a subject or for a day.
домашние задания (plural) – “homework assignments.”
Used when emphasizing multiple separate tasks.
домашняя работа (feminine) – could mean housework (chores at home) or, in context, homework, but for schoolwork домашнее задание is clearer and more standard.

In this sentence делать домашнее задание is the natural, textbook way to say to do (my) homework.

Is the word order fixed? Can I say Иногда лень мешает мне делать домашнее задание or Лень иногда мешает мне делать домашнее задание?

The word order is flexible, and all of these are grammatical, with slightly different focus:

Иногда мне мешает лень делать домашнее задание.
– Neutral, common; мне (to me) is early, so the focus is on how I am affected.
Иногда лень мешает мне делать домашнее задание.
– Now лень (laziness) is earlier, so there is a bit more focus on laziness as the topic.
Лень иногда мешает мне делать домашнее задание.
– Starts with лень, which puts strongest emphasis on laziness: Laziness sometimes prevents me from doing my homework.

All would be understood the same way in everyday conversation; the differences are stylistic / in emphasis.

I often see мне лень делать домашнее задание without мешает. What’s the difference in meaning?

Мне лень делать домашнее задание.
Literally: To me, it’s laziness to do homework → natural translation: I’m too lazy to do my homework / I can’t be bothered to do my homework.
This is a very common, compact expression.
Мне мешает лень делать домашнее задание.
Literally: Laziness gets in my way of doing my homework.
This makes “laziness” sound more like a separate obstacle that is interfering with you.

In everyday speech, Мне лень делать домашнее задание is more frequent. The version with мешает is a bit more descriptive, as if you’re analyzing your behavior: My laziness is preventing me from doing homework.

What is the difference between мешать and помешать in this kind of sentence?

Both mean “to disturb / to hinder / to get in the way,” but aspect is different:

мешать – imperfective, describes an ongoing or repeated situation:
- Иногда мне мешает лень… – Sometimes laziness is (regularly) getting in my way.
помешать – perfective, describes a single completed act of interference:
- Ничто не помешало мне сделать домашнее задание.
  – Nothing prevented me (that time) from doing my homework.

In your sentence, иногда (sometimes) suggests a repeated situation, so мешает (imperfective) is the natural choice.