Наша первая сессия оказалась сложнее, чем мы ожидали.

Because сессия is a feminine singular noun. In Russian, possessive words and adjectives agree with the noun in gender, number, and case.

So in наша первая сессия:

• наша = feminine singular
• первая = feminine singular
• сессия = feminine singular

If the noun were masculine, you would get наш; if neuter, наше.

It is in the nominative case because it is the subject of the sentence — the thing that turned out to be more difficult.

You can think of наша первая сессия as the answer to What turned out to be more difficult?

Сессия can mean different things depending on context. Common meanings include:

• a session
• a meeting/session in therapy, coaching, study, etc.
• in academic contexts, an exam period

So the grammar stays the same, but the exact English translation depends on the situation.

Оказалась is the past tense form of оказаться, and here it means turned out or proved to be.

So:

• сессия оказалась сложнее = the session turned out to be more difficult

This verb is very common when Russian talks about a result that became clear later.

In the past tense, Russian verbs agree with the subject in gender and number.

The subject here is сессия, which is feminine singular, so the verb must also be feminine singular: оказалась.

Compare:

• урок оказался — masculine
• сессия оказалась — feminine
• занятие оказалось — neuter
• сессии оказались — plural

Because оказалась adds the idea of it turned out / it ended up being. It suggests that the real situation became clear only after the fact.

• была сложнее = was more difficult
• оказалась сложнее = turned out to be more difficult

So оказалась is a better choice if you want that sense of discovery or surprise.

Because the sentence is making a comparison: more difficult than we expected.

Сложнее is the comparative form of сложный:

• сложный = difficult / complex
• сложнее = more difficult / more complex

If you used сложная or сложной, you would no longer be expressing the comparison in the same direct way.

Also, comparative forms like сложнее do not change for gender or number, so the same form works with many different subjects.

Here чем means than.

So:

• сложнее, чем мы ожидали = more difficult than we expected

The comma is used because чем мы ожидали is a subordinate comparative clause. In Russian, this is normally separated with a comma.

Yes, Russian can often omit subject pronouns, but here мы is helpful because the past tense form ожидали only shows plural, not person.

By itself, ожидали could mean:

• we expected
• they expected

So adding мы makes the meaning explicit.

Also, ожидали comes from ожидать, which is the normal verb for to expect here.

The object is understood from context. English does the same thing:

• It was harder than we expected

You do not have to repeat it in English, and Russian also does not need to repeat the session or use a pronoun here.

So чем мы ожидали naturally means than we expected it would be.

Yes. Russian word order is flexible, and the original sentence is the most neutral version:

Наша первая сессия оказалась сложнее, чем мы ожидали.

Other word orders are possible, but they change the emphasis. For example:

Сложнее, чем мы ожидали, оказалась наша первая сессия.

This sounds more emphatic or literary, with the comparison highlighted first.

For a learner, the original order is the safest and most natural one to use.